Here are five test vectors for secp256k1, which I just generated with my own code. My code is a generic implementation of elliptic curves; it has been tested for many curves for which test vectors were available (in particular the NIST curves) so I tend to believe that it is correct. Each test vector is a value $m$ (chosen randomly modulo the curve order $n$) and the coordinates $(X, Y)$ of the point $mG$, where $G$ is the conventional generator defined in section 2.7.1 of SEC 2.

For self-testing an elliptic curve implementation, I suggest first verifying that multiplying $G$ by $n$ (the expected curve order) indeed yields the point at infinity. Then, do the following many times:

Choose two random integers modulo $n$; call them $a$ and $b$.

Compute $c = a + b$.

Compute points $P = aG$, $Q = bG$ and $R = cG$.

Verify that $P + Q = Q + P = R$.

If you go through this a few dozen times with no errors then chances are that your implementation is at least mostly correct.

A must-have reference on elliptic curve implementation is the Guide to Elliptic Curve Cryptography. It is not free, but worth its price. Good university libraries will let you read it without spending a dime on it.